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How to Interpret Achievement Test Scores

By Beth Wenbourne Katz

Parents and teachers need to know how to interpret achievement test scores.

Misinterpreted test scores can lead to many problems, including over or underestimating a student's abilities and incorrect academic placements. That's why educators and parents must understand what these scores actually represent. Knowing how to accurately interpret achievement test scores helps teachers and parents get a more accurate picture of student performance.

Interpreting Norm-Referenced Scores

When creating norm-referenced assessments like the Woodcock-Johnson, 3rd Edition, educational researchers administer the test to a large group of students. These students comprise a norm group, and their scores create a standard achievement curve. Later, assessors administer the achievement tests to individual students and report their performance in relation to the norm group. Three common ways to report norm-referenced scores are with age and grade equivalency, percentile ranks and standard scores.

Interpreting Age and Grade Equivalency

Age and grade equivalencies report a student's performance in a simple way: through grade and chronological age. For example, if a student's scores align with the average fifth grader's scores from the norm group, his GE is "5." While this seems simple and straightforward, it is not. In fact, it is common for people to misinterpret AE and GE scores for two reasons. First, they do not compare a student's performance against any set standard -- just the norm group -- so, a student's GE for reading may be "5" according to the test, but he may still not be meeting the fifth grade reading standard set by a state or school district. Also, learning is developmental and more learning takes place in a child's early years, so AE and GE deficits affect younger students more. For example, a student with a six-month AE delay is more profoundly affected if his chronological age is three than if it is 22.

Interpreting Percentile Ranks

Percentile ranks represent the percentage of the norm group that performed higher or lower on a test than an individual student. For example, if a student's achievement test score places him in the 70th percentile, then 70 percent of students in the norm group earned the same score or lower. So, the student's performance is equal to, or higher than, 70 percent of the norm group, and lower than 30 percent of the norm group. When interpreting percentile ranks, it is important not to confuse percentiles with percentages. Percentages refer to the total percent of questions a student answers correctly, while percentiles refer to the comparison of the norm group.

Interpreting Standard Scores

Like age, grade equivalency and percentile ranks, standard scores represent a student's performance compared to that of a norm group. The standard score is simply a numerical representation of the student's performance in relation to the average, or mean. In order to interpret a standard score, you only need to know what the mean is. For example, a common standard score is the Stanine. The Stanine rates a student's performance with a number between one and nine, with four, five and six representing the mean. Any number above six represents above-average performance, while any number below four represents below-average performance.

Interpreting Criterion-Referenced Scores

Interpreting criterion-referenced scores is more straightforward. Most curriculum-based assessments and state standards tests are criterion referenced. These tests have set standards or a set of criteria that a student must meet. Generally, criterion-referenced assessments convert a student's raw scores into a percentage correct. For example, if a student answers five of ten questions correctly, he answered 50 percent correctly. Interpretation of these scores depends on the set standard. For example, a college professor may require a student to answer 80 percent of exam questions correctly in order to pass, and another may require a score of only 70 percent correct.

About the Author

Based in Sacramento, Calif., Beth Wenbourne Katz has been writing about education topics since 2006. Katz has taught in the California public schools, working primarily with students with learning, behavioral and emotional challenges. She holds a Master of Arts in special education from San Diego State University.